You absolutely have a say in what track you want. You'll have some time to learn from instructors from each of the CSO platforms over the course of a few months of Primary and get a better idea of what you might like and what you don't think you'll like, then you'll put in your preferences to your flight commander. Then, depending on your rank in your class (based on tests, flights, and a flight commander ranking), and how many of each track are given to your class from AFPC, you'll be assigned a track.